fix: use pointer instead of long, which won't work on Windows

[eat-swap]

Using sizeof(long) == 4 to tell whether a platform is 32-bit or not is not reliable since LLP64 platforms exists (and specifically, Win64 API, refernece here). This causes problems while trying to port lrzip to such platfroms.

[anon767]

wouldn't be sizeof(size_t) == 4 be more appropriate?